Magnetic sensors have been used for noncontact measurement of current in many technical fields, including the current control for hybrid cars and electric vehicles, charge and discharge control of a battery, power converters in the power electronics field, and smart grids, or for measurement of magnetic field strength of a throttle position, an accelerator position, the torque of an electric power steering system, etc.
Such a magnetic sensor is known to include a magnetic core (magnetic core with a C-shape) with a ring-like shape to enclose a conductor, such as a current line, with a gap formed in part of the ring-like shape, a magnetic detection element, such as a Hall element, disposed in the gap, and a winding (coil) around the magnetic core.
In the magnetic sensor, a magnetic field that is induced in the magnetic core by flowing current through the conductor is detected by the magnetic detection element placed in the gap. A feedback current is allowed to pass through the wiring in order to set the magnetic field in the magnetic core to zero. The feedback current value is converted into a voltage by means of a detected resistance. By using the voltage value, the magnitude of the current passing through the conductor is determined.
In the magnetic sensor with the above-mentioned magnetic core, however, the magnetic core is formed to enclose the conductor, generating a large induced magnetic field in the magnetic core itself. Thus, the amount of current flowing as feedback current increases, disadvantageously resulting in increased power consumption.
For this reason, for example, devices supplied with current from the batteries have various problems, including reduced usable time in a battery after each charge.
On the other hand, for example, as mentioned in Patent Document 1, there is a known magnetic sensor (current sensor) that includes a planar coil with a linear portion having a plurality of current lines arranged in parallel, each of which extends linearly, and one, or two or more magnetoresistive effect element(s) extending in the same direction as that in which the current lines of the linear portion extend.
The magnetic sensor employing this magnetoresistive effect element is designed to detect part (part of the loop in the circumferential direction enclosing the conductor to be measured) of the induced magnetic field generated by the current (detection target current) flowing through the conductor to be measured by means of the magnetoresistive effect element. Then, the magnetic sensor allows a feedback current to flow through the current lines (planar coil) to cancel the detected magnetic field (to apply a magnetic field to the magnetoresistive effect element, the applied magnetic field having identical magnitude and opposite direction to the external magnetic field applied to the magnetoresistive effect element by means of the current to be detected). Based on the magnitude of the feedback current, the magnetic sensor determines the magnitude of the current to be detected.
A magnetic sensor with the structure mentioned above has the advantage of low power consumption compared to the above related art magnetic sensor, which includes a magnetic core enclosing the conductor to be measured.    Patent Document 1: JP 2011-196798 A